HIV wends its wily way inside CD4 cells through an eerily precise three-step process. Here’s how it hppens--and how entry inhibitors stop it

CD4 ATTACHMENT

HIV’s gp120 attaches to the CD4 cell’s CD4 receptor.
BMS-488043, TNX-355 and PR0-542 block this step in different ways.

RECEPTOR BINDING

After gp120 has changed its shape, it binds to another receptor on the CD4 cell, called either CCR5 or CXCR4. Then gp120 changes again, moving aside to expose HIV’s harpoonlike gp41. GSK-140, UK-427 and SCH-690 all block CCR5, while AMD070 blocks CXCR4.

FUSION

After gp41 embeds itself in the CD4 cell’s membrane (3A), its upper tendrils fold down and “zip” into its lower coils (3B), bringing the HIV and CD4 cell close together, then punching a hole in the CD4 cell membrane that grows until HIV empties itself into it. Fuzeon (T-20) mucks up this step.